Electrical cable with element of high tensile strength

ABSTRACT

To minimize the cross-sectional area or the diameter of an electric line that is under tensile stress, a central fibrous element of a carbon fiber bundle is disclosed. This can be designed so it is resistant to the longitudinal entry of water.

FIELD OF THE INVENTION

This invention concerns an electric line with insulation, and with amultiwire conductor or lead of metal that is shaped into a strand orcable and with a fibrous element that has tensile strength arrangedcentrally in the lead.

BACKGROUND OF THE INVENTION

Electric lines of the type described above are already known. Forexample, German Patent 2,519,687 A1 describes a process for producing aline with strands for electric power line connections, etc., whereby athin fiber of spun glass silk is used as a central strand when wrappingthe cable of individual wires. With such lines the stranded linesconsist of about thirty to sixty individual lines twisted together. Thecentrally inserted glass fiber especially increases the tensile strengthof the cable without resulting in any significant increase in thecross-sectional area because it is embedded into the cavity (wedge)between the individual wires in the process of cabling or stranding.

Such a central glass fiber can be removed very easily when processing oncutting machines and leads to disturbance in the work sequence. Inaddition, embedding between numerous individual lines is not permanentif the finished line is bent frequently during use. Then the enclosedglass fiber can easily escape from the stranded cable and break.

This invention concerns the problem of creating an electric line thancan withstand an extreme tensile stress even while having a smallcross-section and that will be easy to produce and easy to process. Inaddition, if desired, it should be designed so it is resistant tolongitudinal penetration of water in a simple and permanent manner.

SUMMARY OF THE INVENTION

This invention creates an electric line that can be designed so it isextremely small and yet can withstand extreme tensile stresses. It canbe produced economically, can be processed further with no problem andcan be designed so it has flexural stability and is sealed with respectto longitudinal seepage of water.

According to this invention the fibrous element consists of a bundle ofcarbon fiber elements (carbon fibers). When the bundle is divided intoat least eight hundred single filaments or even one thousand to twelvethousand monofilaments depending on the design, where each filament hasa maximum diameter of 0.007 millimeters, the carbon fibers can beoptimally distributed in the internal wedges and can fill out all thecavities. The highest tensile force is achieved when the bundle has atwist. To improve processability of the bundle, the carbon fiberfilaments may be shaped into a yarn with a twist of up to sixty d/m(turns per meter). For the same purpose, the bundle may also be providedwith sizing, e.g., a polymer-based sizing or adhesive, to hold theindividual filaments together by gluing, especially at the points ofcontact or line of contacts with each other. Such a sizing can beapplied by the manufacturer of the bundle. In the simplest design, theconductor or lead is composed of a ring-shaped layer of at least sixindividual wires, that surround the bundle with a radial pressure, sothe internal wedge is completely filled up by the individual filamentsof the bundle.

Additional wires or other line elements can also be applied over thelayer of individual wires. With increased demands of the line, thebundle can be filled with a liquid, paste or powdered material. Such afilling material greatly reduces the friction occurring between theindividual filaments, so it has a positive effect on the flexibility ofthe line and on the stability of the filaments under bending stresses.Filling compounds that also cause a longitudinal sealing of the line canalso be used in that they form a barrier to liquid by swelling, foamingor by some other reaction on exposure to water or any other liquid. Suchfillers are available based on vaseline, petrojelly, silicones,cellulose and other materials. A process for producing a line accordingto this invention provides for at least one layer of wires to bestranded or cabled around a central bundle of carbon fiber filaments insuch a way that these wires are in close contact with the bundle, andthe insulation is arranged around the wires. Then other layers of wiresor other line components can be introduced between the wire layer andthe insulation, e.g., for the purpose of reinforcement, shielding, etc.

To produce a filled line, at least one layer of wires is cabled around abundle of carbon fiber filaments provided with a filling compound insuch a way that the wires are in close contact with bundle andinsulation is provided around the wires under a radial pressure so thatall outside wedges of between wires are filled. The bundle can be filledby guiding it through a filling device directly before applying thewires and the bundle is impregnated and coated with the fillingcompound. If additional line elements are introduced, they must eitherbe free of cavities or must also be provided with a correspondingfilling compound.

It is advisable to guide the bundle directly, before applying the(first) layer of wires, through a filling system where the bundle isimpregnated with the filling compound.

A complete understanding of the invention may be obtained from thedetailed description that follows taken with the accompanying drawings.

DESCRIPTION OF THE DRAWINGS

The Figures show one practical example of this invention, which isdescribed in greater detail below. The line according to this inventionis compared with a traditional line of the same tensile strength. FIG. 1shows a traditional electric line in cross-sectional view. FIG. 2 showsan electric line according to this invention in cross-sectional view.FIG. 3 shows a detail of the central fibrous element with threeindividual filaments.

BEST MODE FOR CARRYING OUT THE INVENTION

FIG. 1 shows an electric line 1 that consists of a cabled copper strand2 of nineteen wires 3 laid in a design of 1+6+12 wires with a diameterof 0.18 mm and insulation 4 of polyvinyl chloride. The diameter of theline is 1.5 mm, its cross-sectional area is 1.77 mm². The totalcross-sectional area of the nineteen wires is about 0.5 mm², and thetensile force is about 130 newtons.

There are applications where such line cross-sections are selectedmerely for reasons of tensile stress and/or flexibility. A much smallerline cross-section would be sufficient for electric transmission.

FIG. 2 shows an electric line 10 that consists of a central carbon fiberbundle 11 with a diameter of about 0.2 mm consisting of about 1000monofilaments 12 with a diameter of about 1/7000 of a millimeter each.The individual filaments 12 have a polymer-based sizing 13 that causesthe individual filaments 12 to adhere to each other and it also has atwist of about 7 d/m (turns per meter).

Bundle 11 is surrounded by a layer 14 of six copper wires 15. The copperwires 15 have a diameter of about 0.2 mm, resulting in a totalcross-sectional area for the six wires of about 0.2 mm². All thecavities within layer 14 of wires 15 and between the individualfilaments 13 of bundle 11 are filled by a filling agent 16 based onvaseline.

Layer 14 of copper wires 15 is surrounded by an insulation 17 ofpolyvinyl chloride, which completely fills up the outer wedge 18. Thediameter of line 10 is 1.19 mm, and its cross-sectional area is 1.11mm². The tensile force is 120 Newtons.

The new line thus has a diameter that is reduced by about twenty-onepercent at approximately the same tensile force, and the cross-sectionalarea is reduced by thirty-eight percent. These are values that can be agreat advantage in cases where it is important to save space or weightand thus these values can constitute an important advantage. These newlines can be processed further with no problem because the centralcarbon fiber does not cause any interference. Stripping the insulation,crimping, welding and soldering can be performed without any negativeeffects, so this line is especially suitable for producing cable sets ofall types.

To produce line 10 the six copper wires 15 and carbon fiber bundle 11are sent to a cabling device. Before the cabling point, the bundle 11 isfilled with a filling compound and coated in a stuffing device. Thewires 15 are cabled around the central bundle 11 in the cabling device.The monofilaments 12 of bundle 11 have an individual length of twist ofabout 15 mm and the bundle is compressed radially, so all the insidewedges and all of the space enclosed by wires 15 is filled by bundle 11,i.e., by the individual filaments 12 and the filling compound 16. Thenthe stranded cable thus produced is passed through an extruder andcoated with plastic insulation 17 such as PVC under a radial pressure.In doing so, the insulation material fills up all the outer wedges 18 sothat no cavities are left.

The embodiment described here illustrates only a simple application ofthis invention. This invention can also be used for multiline round orflat lines that can serve a variety of purposes, e.g., for powertransmission or communications transmission, for control purposes ormeasurement purposes.

Since carbon fibers conduct electricity, they cannot develop anyinterfering insulation layers at the contact points as is the case withother nonmetallic reinforcing fibers.

Although the description of this invention has been given with referenceto a particular embodiment, it is not to be construed in a limitingsense. Many variations and modifications will now occur to those skilledin the art. For a definition of the invention reference is made to theappended claims.

What is claimed is:
 1. In an electric line of the type comprising amultistranded cable of metal wires, a central fibrous element forproviding tensile strength to the line and being disposed in the centerof the cable and a layer of insulation around the cable, the improvementwherein the fibrous element is formed from a bundle of carbon fiberfilaments, said bundle comprises at least eight hundred carbon fiberfilaments each of which has a diameter of 0.007 millimeter or less, saidbundle has a twist of zero to twenty turns per meter and being providedwith a sizing that holds the individual filaments together, said cablehas a ring-shaped layer of six individual wires that surround saidbundle with the space within the wires being optimally filled by thefiber filaments, and said layer of insulation surrounds said ring-shapedlayer and fills the outer space between the wires.
 2. An electric lineaccording to claim 1 wherein said bundle is impregnated with a fillingcompound for forming a barrier to a liquid on exposure to said liquid bya reaction thereto.
 3. An electric line according to claim 1 whereinsaid ring shaped layer of six individual wires exert a radial pressureon said bundle.